Human CXCL1 is a kind of chemokine belonging to the CXC family. In blood, this protein is present in blood platelets and is known to be over-expressed upon inflammation reactions in a manner similar to that of other members of the CXC family.
In recent years, it has been reported that human CXCL1 functions as a tumor-related factor. Therefore, it is expected that human CXCL1 can serve as a urothelial cancer marker through quantitative detection of human CXCL1 in urine (Hiroaki Kawanishi et al, 2008, Clinical Cancer Research, vol. 14, No. 9, 2579-2587; and WO2007/026895). It has been further reported that the amount of human CXCL1 fluctuates at the gene level and at the protein level in the tissue or blood of patients with other malignant tumors such as large-bowel cancer, ovary cancer, or malignant melanoma (Gong Yang et al, 2006, PNAS, vol. 103, No. 44, 16472-16477; Yu Wen et al, 2006, Clinical Cancer Research, vol. 12, No. 20, 5951-5959; and Jing Luan et al, 1997, Journal of Leukocyte Biology, vol. 62, No. 5, 588-597). The human CXCL1 potentially enables extremely early and/or early detection of such cancers, in addition to urothelial cancer.
However, measurement methods using an existing enzyme immunoassay have insufficient sensitivity for detection of the above cancers. For example, WO2007/026895 discloses a kit for measuring human CXCL1 produced by R&D SYSTEMS, Inc. (hereinafter, R&D SYSTEMS), wherein, although the detection limit concentration is around 20 pg/mL, the concentration of human CXCL1 in the urine of a healthy subject does not reach the detection limit. Hence, a method for measuring human CXCL1 with higher sensitivity has been desired.